It is known to use carbon blacks of various specifications as components of elastomer mixtures. These are added less for the purpose of making the resultant vulcanizates less expensive than to optimize their overall properties for various applications. Among these are, above all, tear strength, modulus of elasticity, hardness, tear propagation resistance and abrasion resistance. Carbon black is thus designated as a so-called active or reinforcing filler.
However, the use of carbon black in elastomer mixtures is limited for various reasons. On the one hand, only black mixtures or in any event no colored or white mixtures, can be manufactured. On the other hand, good carbon blacks have become quite expensive compared with economical mineral fillers, such as silicic acid (SiO.sub.2), kaolin, aluminum hydroxide and glass. As a result, increasing efforts have been made to replace carbon black by fillers, such as those recited above, all of which are also light colored. Such replacement has the further significant advantage of reducing the proportion of components based on crude oil, which is subject to supply crises. Moreover, the utilization of highly active silicic acids is of great advantage for optimizing certain properties, such as, for example, notch impact strength.
Such light-colored mineral fillers have been used in the past primarily only from an economic viewpoint. Initially, considerable impairment in important end use properties had to be tolerated, such as, for example, impairments in heat degradation, elasticity, and compression set. Similar problems also exist in the filling or reinforcement of other polymeric materials with mineral fillers, for example polyolefins or unsaturated polyester resins.
These disadvantages have been overcome at least partially by the use of so-called adhesion promoters. Generally speaking, these are compounds exhibiting a certain affinity to the polymer as well as to the filler, preferably by entering into a chemical reaction with the two substrates.
Especially well-known adhesion promoters are the organofunctional silanes. They have the formula R-SiX.sub.3 wherein X in most cases is alkoxy and less frequently is halogen, and the organic residue R is an alkyl or aryl group substituted by a functional group. These compounds yield polymer-filler combinations having satisfactory properties; nevertheless, they do exhibit several disadvantages in use. For example, various silanes can be optimally used in vulcanizable elastomer-filler mixtures only for a specific type of crosslinking technique in each case. Unpleasant odors also occur, for example, when using the mercaptosilanes. Moreover, the mixtures crosslinked by the silanes tend toward premature vulcanization (scorch). Furthermore, compared with the other components of the elastomer mixtures, organofunctional silanes are extraordinarily expensive and generally exhibit a toxicity with respect to inhalation and skin contact which cannot be ignored.
A number of attempts have been made to achieve similar effects of the adhesion promoters by synthesizing them on a polymeric basis. For example, natural rubber and styrene-butadiene elastomer (SBR) can be hydrosilylated by heating with trichlorosilane to about 300.degree. C. (U.S. Pat. No. 2,475,122); such reaction products adhere well to glass plates (U.S. Pat. No. 2,557,778).
The photochemical hydrosilylation of a liquid polybutadiene obtained by anionic polymerization is described in U.S. Pat. No. 2,952,576, which relates to glass fibers coated with this material for the reinforcement of unsaturated polyester resins. The microstructure of the liquid polybutadiene is not mentioned. However, from the details of its production from a sodium suspension, in conjunction with a comparison of data from the literature, it can be concluded that this polymer contains about 60-70% of vinyl groups, 30-20% of trans-vinylene groups and only about 10% of cis-vinylene groups.
The catalysis of hydrosilylation of polybutadienes by platinum compounds is described as an intermediate stage in the production of foam stabilizers or laminating resins, respectively, in DOS's [German Unexamined Laid-Open Applications] 1,620,934 and 1,720,527. These DOS's do not suggest the use of the reaction products in connection with rubber-filler mixtures. Furthermore, as above, both cases involve products having a high content of vinyl groups, the remaining double bonds consisting predominantly of trans-vinylene groups. Polybutadienes of such microstructure exhibit a very high viscosity at room temperature even at relatively low molecular weights; as a result of this consistency, their handling, dosing, and intermixing are extraordinarily difficult. The same limitation applies to their hydrosilylated derivatives.
The conventional Pt catalysis of the hydrosilylation is also described in U.S. Pat. No. 3,759,869 whose polymers have molecular weights of between 500 and 50,000 and contain to an extent of at least 25% by weight the structure ##STR2##
In the case of pure polybutadiene as the basic polymer, this provides a reactive silyl group --SiX.sub.3 at about each tenth monomer unit. The examples merely disclose the hydrosilylation of a polybutadiene having an average molecular weight of 1,000 and a vinyl group content of 90%, based on the total number of double bonds, with practically 100% saturation of all vinyl groups present. Mixtures of such products and/or their derivatives obtained by secondary reactions with low molecular weight polypropylene (molecular weight 5,000) or EPM elastomer are merely mentioned without anything being said about their effectiveness. Additionally, these most extensively saturated polybutadiene derivatives and/or fillers provided therewith solely due to the lack of double bonds are only poorly suited for forming a composite with a polymer network produced by sulfur or peroxide vulcanization.
DOS No. 2,343,108 claims the hydrosilylation of elastomer polymers containing, preferably, at least 5-30% by weight of vinyl groups, and their use as coupling agents for the vulcanization of a vulcanizable elastomer comprising a silicic-acid-containing pigment. These are products which can only be used in solution due to their high molecular weight.
In contrast, DAS [German Published Application] No. 2,635,601 describes hydrosilylation products of specific polybutadiene oils with molecular weight of 400-6,000, which, thanks to their microstructure (10-60% vinyl groups, 1-15% trans-vinylene groups, and 25-85% cis-vinylene groups), exhibit particularly low viscosities and thus can be handled readily in undiluted form. However, the hydrosilylation products have the disadvantage that the platinum catalyst used during their manufacture extensively remains in the product and thus is lost.
The reaction of lithium-terminated "living polymers" with an excess of a tetrahalo- or tetraalkoxysilane is described by U.S. Pat. No. 3,244,664. This excess, which must be employed to avoid coupling or crosslinking reactions, is practically inseparable and, accordingly, is lost to further processing.
Furthermore, German Patent Application No. P 30 10 113.4 discloses homo- or copolymers carrying reactive silyl groups, made from 1,3-dienes, which contain 0.4-9% by weight of bound silicon and are obtained at a temperature of 0.degree.-80.degree. C. by reating a metallized 1,3-diene homo- or copolymer having a molecular weight (Mn) of 400-8,000 with a silicon compound of the formula ##STR3## wherein X.sup.1 is halogen or alkoxy,
X.sup.2 is a hydrolyzable group, PA0 Y and Z can be identical to X.sup.2 but can also be hydrogen, alkyl of 1-8 carbon atoms, cycloalkyl of 5-12 carbon atoms or optionally substituted phenyl. PA0 X is a hydrolyzable residue, PA0 Y and Z are the same as X, hydrogen, or alkyl of 1-8 carbon atoms, cycloalkyl of 5-12 carbon atoms, or an optionally substituted phenyl residue. PA0 X is a hydrolyzable residue, PA0 Y and Z independently are X, hydrogen, an alkyl residue of 1-8 carbon atoms, a cycloalkyl residue of 5-12 carbon atoms, or an optionally substituted phenyl residue, PA0 0-60% vinyl groups PA0 1-25% trans-vinylene groups PA0 In addition, up to 40% alicyclic structures can be present.
The addition of sulfhydryl groups of a mercaptosilane, e.g., .gamma.-mercaptopropyltriethoxysilane, to double bonds of an unsaturated polymer has been repeatedly described (e.g., in U.S. Pat. No. 3,440,302, DOS's Nos. 2,333,566 and 2,333,567), but has the disadvantage of a very expensive and foul-smelling starting material.
Furthermore, processes are known which produce polymers having reactive silyl groups by using silyl-group-containing peroxy compounds (DOS's Nos. 2,152,295 and 2,152,286) or azo compounds (J. Appl. Pol. Sci. 18: 3259 [1974]) as the initiators or by using silyl-group-containing disulfides (DOS No. 2,142,596) as chain-transfer agents of the radical polymerization. Here again, the auxiliary agents used to introduce the silyl groups are only accessible with difficulty, are very expensive, and in most cases, are not commercially available at all. In addition, a maximum of two reactive silyl groups, i.e., at the ends of the polymer chain, can be introduced in this way. Products with a higher silicon content, which may be desirable for obtaining certain effects such as increased self-crosslinking ability, consequently, cannot be produced.
Silyl-group-containing polyalkenamers can be readily prepared using silyl olefins (German Pat. No. 2,157,405) or silyl cycloolefins (DAS No. 2,314,543) as regulators or (co-) monomers in the ring-opening polymerization of cycloolefins; however, the economic availability of these reactants is also a limiting factor for general application.
Finally, homo- or copolymers of 1,3-dienes carrying reactive silyl groups, are known from German Patent Application No. P 30 03 893.8, corresponding to U.S. Application Ser. No. 230,483, filed on Feb. 2, 1981, whose disclosure is incorporated by reference herein. These contain 0.4-12% by weight of bound silicon and are obtained by reacting, at a temperature of 190.degree.-300.degree. C., a 1,3-diene homo- or copolymer, containing more than 1% of its aliphatic double bonds in conjugation and having a molecular weight (Mn) of 400-6,000, with a silicon compound of the formula ##STR4## wherein R is an unsaturated cyclo or acyclic aliphatic hydrocarbon residue of 2-20 carbon atoms,